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mcDESPOT Repeatability at 3T. March 25, 2012 Jason Su. Questions. ASSET vs. ARC: How do parallel imaging artifacts propagate through to the maps? Is mcDESPOT w/ B-S B1 correction a repeatable experiment at 3T? What is the effect of inaccurate B1 on each of the maps?
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mcDESPOT Repeatability at 3T March 25, 2012 Jason Su
Questions • ASSET vs. ARC: How do parallel imaging artifacts propagate through to the maps? • Is mcDESPOT w/ B-S B1 correction a repeatable experiment at 3T? • What is the effect of inaccurate B1 on each of the maps? • How do the maps compare to 1.5T? • Does MWF remain the same? We would hope it would but does not for UBC group’s MWF
Scanning • 1 volunteer • 2 scans, baseline and follow up exactly 24 hours later • Acceleration: 70% partial k-space, ASSET 2 or ARC 2x1.5 • B-S: TR 500ms, BS FA 270 deg., 32x32 22cm FOV, 6mm slice • Day 0 – no HOS • 8ch head coil: ASSET, ARC • 32ch head coil: ASSET • Day 1 – some HOS • 8ch head coil: ASSET (SSFP HOS), ARC (HOS) • 32ch head coil: ASSET (no HOS), ARC (no HOS) • 6:30 for one complete mcDESPOT protocol at 2mm isotropic
Post-Processing • B-S B1 maps via updated Orchestra recon • Converted to flip angle then “kappa” maps • xmtAddScan and xmtAddFTG are stored in header for efgre3d22M4v04 • Need to add ia_rf1 to header, assuming now that = 32767 when xmtAddScan < 200, otherwise unknown (thankfully not the case) • Linear interpolation from 27 to 80 slices • 3T2 protocol expiry? Interest in getting it running at Sherman and 3T3. • Registration to intermediate “halfway” space • Distributes interpolation errors/blur equally between two volumes • Allows for much better voxelwisecomparison • White matter segmentation is performed with FSL FAST on the registration target • The mask is then eroded with a spherical kernal of radius 2mm to stay away from possible GM edges
ASSET vs. ARC • Images and maps are presented without B1 correction • Would have added an additional variable and not needed for this comparison • Artifacts are more prominent in ASSET • Clear skull aliasing artifact running through center of images • How do parallel imaging artifacts propagate through to the maps?
Conclusions • 32ch coil seems to give less consistent results than 8ch for ARC vs. ASSET • Artifacts are more apparent with 32ch (surprising?) and are responsible for higher percent difference than 8ch • 8ch SPGR images appear better with ASSET • MWF seems less affected by the artifacts than T1 and T2, or at least harder to see
Repeatability • Is mcDESPOT w/ B-S B1 correction a repeatable experiment at 3T? • Will show 8ch ASSET, 8ch ARC, 32ch ASSET • 32ch ARC was not collected at baseline
